CN1224531A - High pressure gas discharge lamp - Google Patents

Abstract

This invention relates to a high-pressure gas discharge lamp with a maximum rated power of 100 watts. The lamp is equipped with a discharge capacitor having a translucent ceramic wall thickness of d. Two electrodes, each having an electrode head, are arranged in the discharge capacitor surrounded by the wall at a distance of EA between the electrode heads. The discharge capacitor contains an ionizable filler comprising at least sodium (Na) and halides. According to the invention, the wall thickness is at least 1 mm.

Description

High pressure gas discharge lamp

The invention relates to a high-pressure gas discharge lamp with a rated power of up to 100 watts provided with a discharge vessel enclosing a discharge space with a translucent ceramic wall thickness d, with two electrodes each provided with an electrode tip and with said electrodes the heads are arranged in said discharge space at a mutual distance EA, said discharge vessel contains an ionizable filling comprising at least sodium (Na) and a halide, and said discharge vessel is cylindrical within said distance EA and has a cross-sectional inner diameter Di.

A lamp of the type mentioned in the opening paragraph is known from European patent EP215524 (N 11.485). This known lamp with a rated power of 40 W has a discharge wall thickness of 0.45 mm. The ionizable filling of the discharge vessel comprises, in addition to mercury (Hg), halides of Na, thallium (Tl) and indium (In). The lamp has good color properties, in particular a good color point expressed with coordinates (x;y) and good values for both the general color rendering index Ra and the color rendering index R ₉ representing the reproduction of red. This makes the lamp intrinsically well suited for interior lighting applications. The following recognized techniques are utilized in this lamp: good color rendering is possible when Na halides are used as constituents of the lamp's fill; and the pressure of Na during lamp operation is so high that Na-D lines appear Strong broadening and inversion of Na emission. Due to the presence of excess Na, a high coldest spot temperature _Tcs in the discharge vessel is required during lamp operation, eg 1000K (730°C). In the case of Na–D line inversion and broadening, they assume in the spectrum the shape of emission bands with two maxima at a mutual distance Δλ. The requirement that _Tcs should have a high value practically precludes the use of quartz or quartz glass for the discharge vessel wall, and a ceramic material must be used.

In the present description and claims, the term "ceramic wall" is understood to mean both a gas-tight wall of a metal oxide, such as sapphire or densely sintered polycrystalline Al ₂ O ₃ , and a wall made of a metal nitride. , for example walls made of AlN.

A disadvantage of the known lamps is that they have a relatively short life in practice due to chemical attack of the discharge vessel and rupture of the discharge vessel.

It is an object of the invention to provide measures for realizing a lamp with a long service life. To this end, a lamp of the type mentioned in the opening paragraph is characterized in that the thickness of the wall is at least 1 mm.

The use of thicker walls not only advantageously leads to a better heat transfer from the wall part between the electrodes to the cooler end of the discharge vessel, but also especially to an increase in the heat rays emitted by the walls of the discharge vessel. The thick wall here leads to a lower temperature and a smaller temperature gradient across the wall compared to a wall according to the prior art. The latter has a particularly favorable effect on slowing chemical processes in which the migration of components plays a major role. It is true that a thicker wall inherently leads to less chemical attack and less risk of cracking, but, on the other hand, it leads to a reduction of the coldest spot temperature T _cs , keeping all other parameters constant. It has been found in known lamps that the color properties, especially the color point and the color rendering index in general, are very sensitive to variations in T _cs .

In an advantageous embodiment of the lamp according to the invention, this reduced sensitivity to changes _{in Tcs} is largely achieved due to the fact that the ionizable filling does not contain In. A further improvement is achieved due to the fact that the ionizable filling comprises a rare earth halide. The color stability over the entire life of the lamp is thus also considerably improved. In this regard, dysprosium (Dy) has been found to be a particularly suitable constituent of the ionizable filling.

In a lamp according to the invention, the following relationship is preferably observed: 0.4≦EA/Di≦1.5. The advantage of observing this relationship is that despite the wall thickness, the T _cs value is still in the range between 1200K and 1300K, while at the same time the maximum temperature of the discharge vessel wall is still limited to 1400K. It has been found experimentally that for values of _Tcs in the range from 1200K to 1300K, values of Δλ between 12 nm and 60 nm can be achieved. In order to realize a lamp that radiates white light with a general color rendering index of at least 90, the value of Δλ is preferably between 12 nm and 60 nm.

For a ratio of EA/Di≦0.4, it has been found that due to the convection in the lamp vessel, a considerable blackening of the discharge vessel wall occurs within a comparatively short time. This blackening is disastrous for the good color characteristics of the lamp. On the other hand, if said ratio is chosen to be greater than 1.5, it has been found in practice that it is impossible to combine values of the general color rendering index greater than 90 with a long lamp life without an unacceptable loss of luminous efficiency .

The above and other aspects of the lamp according to the invention will be explained in more detail below with reference to the accompanying drawings (not to scale) in which:

Figure 1 schematically shows a lamp according to the invention, and

FIG. 2 shows the discharge vessel of the lamp of FIG. 1 in detail.

1 shows a metal halide lamp with a discharge vessel 3 having a ceramic wall thickness d surrounding a discharge space 11 containing an ionizable filling comprising at least Na and halides. Two electrodes whose electrode heads are at a mutual distance EA are arranged in the discharge vessel, which is cylindrical at least in the region of the distance EA and has a cross-sectional inner diameter Di. The discharge vessel is plugged at one end with a ceramic protruding plug 34, 35 which surrounds with a narrow insertion gap the current input conductors connected to the electrodes 4, 5 arranged in the discharge vessel (Fig. 2: 40, 41, 50, 51), and the ceramic protruding plug is connected in a gas-tight manner to the electrode at the end remote from the discharge vessel by means of a fused ceramic seal (Fig. 2: 10). The discharge vessel is surrounded by an outer bulb 1 with a lamp cap 2 arranged at one end. A discharge extends between electrodes 4 and 5 when the lamp is in operation. The electrode 4 is connected via a current conductor 8 to a first electrical contact forming part of the burner 2 . The electrode 5 is connected via a current conductor 9 to a second electrical contact forming part of the burner 2 . The discharge vessel shown in more detail (not to scale) in FIG. 2 has a ceramic wall and consists of a cylindrical part with an inner diameter D _i and bounded at both ends by end wall portions 32a, 32b, the end The wall portions 32a, 32b each form an end face 33a, 33b of the discharge space. The end wall parts each have an opening in which a ceramic protruding plug 34 , 35 is fixed in a gas-tight manner by means of a sintered node S in the end wall part 32 a , 32 b . The ceramic extension plugs 34 , 35 each tightly surround the current input conductors 40 , 41 , 50 , 51 of the corresponding electrodes 4 , 5 with electrode heads 4 b , 5 b. The current input conductors are connected in a gas-tight manner to ceramic extension plugs 34 , 35 at the ends remote from the discharge space via fused ceramic connection parts 10 .

The electrode heads 4b, 5b are positioned at a mutual distance EA. The current input conductors each have a respective part 41, 51 in the form of a highly halide-resistant ceramic alloy, for example Mo—Al ₂ O ₃ , and are fixed in a gas-tight manner to a respective end plug 34 by means of a fused ceramic connecting portion 10, 35 parts 40,50. The fused ceramic connection extends over the Mo ceramic alloy 41 , 51 for a distance, eg 1 mm. It is also possible to form parts 41 , 51 in forms other than Mo—Al ₂ O ₃ ceramic alloys. Another possible structure is known, for example, from European patent EP-0587238 (US patent US-A-5424609). A particularly suitable structure was found to be a very halide resistant coil wound around a needle which is also very halide resistant. Mo is very suitable as said very halide-resistant material. The portions 40, 50 comprise a metal whose coefficient of expansion closely matches that of the end plug. Niobium (Nb), for example, is a very suitable material for this purpose. Said parts 40, 50 are respectively connected to respective current conductors 8, 9 in a manner not shown in any detail. The input structure allows the lamp to work in any ignition position.

Each electrode 4, 5 comprises an electrode rod 4a, 5a equipped with a coil 4c, 5c close to its electrode head 4b, 5b. The ceramic protruding plugs are fixed in the end wall parts 32a, 32b in a gas-tight manner by means of sintered nodes S. Here, the electrode head is located between the end faces 33a, 33b formed by the end wall parts. In another embodiment of the lamp according to the invention, the ceramic protruding plugs 34, 35 are recessed relative to the end wall portions 32a, 32b. In that case the electrode tips lie substantially in the plane of the end faces 33a, 33b formed by the end wall parts.

In a practical implementation of a lamp according to the invention as shown in the accompanying drawings, the rated lamp power is 40 watts and the lamp has a rated lamp voltage of 95 volts. The translucent wall of the discharge vessel had a thickness of 1.2 mm. The internal diameter Di of the discharge vessel is 4 mm. The interval EA between the electrode tips is 4 mm. The ionizable fill of the lamp comprised 3 mg Hg and 7 mg (Na+Tl+Dy) iodide with molar compositions of 83.6%, 7.2% and 9.2%, respectively. The discharge vessel also contained argon (Ar) at 300 mbar for accelerated ignition. During lamp operation, the value of T _cs is 1265K. After 100 hours, the lamp emitted light at a luminous efficacy of 77 lumens/watt. The color temperature T _c of the radiated light is 2914K, and the color point coordinates (x; y) are (0.443; 0.406). The general color rendering index Ra is 92, the value of the index _R9 is 31, and the value of Δλ is 12.9 nm. After working for 1000 hours, the luminous efficiency is 63 lumens/watt, T _c is 2780K, Ra is 93, R ₉ is 40, and (x; y) is (0.454; 0.411). After 4500 hours of operation, the quantities have the following values: 55 lumens/watt; 2752K; 93; 38; and (0.455; 0.409). After 10000 hours, values were measured for the above quantities: 50 lm/W; 2754K; 92; 30; and (0.454; 0.407). During this process, the value of Δλ changed only slightly, rising to 13.3 nm. After 14000 hours of operation, the discharge vessel showed no cracks or gas leaks due to chemical attack of the discharge vessel walls. A comparative lamp whose discharge vessel had a wall thickness of 0.9 mm had reached the end of its life after 2500 hours due to gas leakage from the discharge vessel. A similar lamp with a wall thickness of 0.6 mm already leaked gas from its discharge vessel after reaching 2000 hours. In a comparative lamp whose ionizable fill contained In instead of a rare earth halide, the color point changed from an initial (0.429; 0.417) to (0.467; 0.422) after 2000 hours of ignition time. The Ra value is only 80 and R ₉ <0.

A wall thickness of 1.6mm or more does achieve a long lamp life (14000 hours ₎ , however, it results in a low _Tcs value (<1200K) which is relatively low so that at the beginning of the lamp life Generally, the value of the color rendering index Ra is lower than 90. Such low values of T _cs also lead to a relatively wide drift of the color point during the lifetime of the lamp.

In another practical implementation of the lamp according to the invention as shown in the attached figures, the nominal lamp power is still 40 watts. However, the inner diameter Di of the discharge vessel was 5 mm, and the electrode tip interval EA was 3 mm. The thickness of the translucent walls of the discharge vessel and its metal halide filling are the same as in the previous examples. The following optical parameters were measured for the described lamps operated with self-induction ballasts:

Color temperature T _c 2740K

General color rendering index Ra 93

Color rendering index R ₉ 79

Color point (0.449; 0.397)

Luminous Efficiency 68 Lumens/Watt

Δλ 19.6 nm

In another practical implementation, a lamp rated at 70 watts was manufactured. In the first lamp, the inner diameter Di was 6 mm and the electrode tip spacing EA was 4 mm. After working for 100 hours and 3700 hours, the color temperature values T _c are 2980K and 2905K respectively, and the color point coordinates are (0.435; 0.398) and (0.441; 0.401), respectively. At these two moments, the general color rendering index Ra is 96 , while the color rendering indices _R9 are 80 and 81, respectively. The luminous efficacy values at said instants were 80 lumens/Watt and 60 lumens/Watt, respectively.

In the second lamp, the EA value was increased to 5mm compared to the first lamp. The measured values after working for 100 hours are: T _c 2908K, (x; y) (0.442; 0.403); Ra 93; R ₉ 40, and the luminous efficiency is 83 lumens/watt. After 3700 hours of operation, the values for the same parameters were: 2837K; (0.447; 0.403); 93; 42; and 67 lumens/watt.

Claims (4)

1. high-voltage gas discharging light with rated power of maximum 100 watts, it has and surrounds discharge vessel discharge space, that its translucent ceramic wall thickness is d, the form that two electrodes that have electrode tip separately are EA with described electrode tip phase mutual edge distance is arranged in the described discharge space, described discharge vessel contains and comprises sodium (Na) and halid ionizable fill at least, and described discharge vessel is columniform in apart from the EA scope and has cross sectional inner diameter Di that described it is characterized in that: the described thickness of described wall is at least 1 millimeter.

2. the lamp of claim 1, it is characterized in that: described ionizable fill does not contain In.

3. claim 1 or 2 lamp, it is characterized in that: described ionizable fill comprises rare earth halide.

4. claim 1,2 or 3 lamp is characterized in that observing following relation: 0.4≤EA/Di≤1.5.

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